Author
Topic: Can helium be used to protect elements such as potassium or phosphorous? (Read 2758 times)

Hello lads n' gals, I'm starting up my elemental collection project again, this time a bit more serious though. So what I am wondering is this; Can I use Helium to protect certain elements, such as potassium, phosphorous etc in an ampule to protect them or is argon way better? I have never seen anyone use helium, and everyone seems to use argon. But argon is quite expensive comparatively and I do not know where to get it legally.

And also: Any good tips on melting the tips of ampules while keeping a gas inside it, mostly helium if that indeed works, but also stuff like chlorine and bromine? I have never so far handled ampules, so any suggestions considering this would be great!

Helium should be more inert than argon is (neon would work too). The main problem with helium is that it is so light. Argon is heavier than air, so it will do a better job keeping air out of the ampoule before it is sealed. Helium will also leak faster than argon (argon is 10 times as massive, so will leak at ~1% the rate of helium.)

It is easiest to seal an ampoule under vacuum (assuming you have the right setup), even for volatile elements like chlorine and bromine, which can be frozen with liquid nitrogen before evacuating the ampoule for sealing.

Of course, if you have never handled ampoules, I have to warn you that sealing them can be dangerous (that rule about never heating a sealed glass vessel kinda goes out the window when you are heating a glass vessel to seal it! Unfortunately the danger doesn't go out the window too) Definitely use safety glasses and possibly also a face shield, especially for the volatile/corrosive/reactive samples!

Yes indeed, the fun is from making the samples myself, a story behind each one!

Do the gasses leak? Even from sealed glass ampules? This seems.. unlikely? How do the atoms diffuse through a solid crystal wall?Sadly no, I do not have equipment to create a vacuum in my tiny apartment, even without a vacuum chamber though it sounds like a good idea to freeze halogens before adding them to the ampules, as long as they don't blow up in my face once they warm up.

But I thank you for the information, I am going to try and get a hold of some argon!

If the ampoule is well-sealed and thick everywhere leakage shouldn't be a problem. However, glass is not crystalline, it is an amorphous solid, and very small species such as hydrogen and helium can pass through imperfections in the structure of the glass, and will be especially problematic if the glass is really thin anywhere.

There is a paper from 1954 (http://scitation.aip.org/content/aip/journal/jap/25/7/10.1063/1.1721760) which describes the measurement of the rate of diffusion (not effusion) of helium through pyrex glass at several temperatures (including room temperature) and found the rates. I made a mistake in my last post. Argon will effuse at 1% the rate of helium, but diffusion is even more sensitive to the size of the atom—they found argon to diffuse through pyrex 100000 times more slowly than helium.

For instance, at 27°C they found D = 7.74×10–9 cm2/second. So if you have an ampoule you can model it as a cylinder using the equations that I have attached, and plug in this D value.

Pure argon.. this is readily available from welding suppliers and is pretty cheap

I dont know how you would go about getting pure gases into the ampules.. but I seem to remember there being glass cylinder kits that I used when sampling gasses, which used a vacuum to draw the gas through and had a spot melting nib on the end to ensure no gas escaped by melting the nibs you had open.

You can modify a bicycle pump to draw a vacuum.. or simpler have a plastic bottle in water and pull upwards.. (if you want me to draw it.. that wont help my drawings are terrible!) with a hose connected to the ampule.. (although this seems like you need five hands!)

Thanks for the replies! I had no idea gases could leak out through glass like, quite an interesting read! Though, as you say it is very dependent on the size of the atom, and it is oxygen that I want to keep out which is as you know quite a bit larger than helium, so it should't be that much of a problem, should it?

I'll look again into getting some argon instead, perhaps I misread some stuff.I am building a little chamber to evacuate all the air by blowing another gas - whatever inert gas i can get - through it, pushing away the good ol' regular air away, kind of like a fume hood! I might take a picture of the complete chamber once it is finished and put it up, if it works like I hope it will.But the general idea is that I will have a chamber that will be simply filled with an inert gas, and at this point I simply seal my ampule inside the chamber

2) Your method of displacing the air in a chamber with an inert gas does not sound practical. You will need a torch to melt the ampoule shut, and unless you supply oxygen, the flame will not work so well in an argon (or helium) environment. In practice a small "argon shower" can accomplish a similar effect (blowing argon through a funnel around what you want to protect from the air), but this should only be done in areas with great ventilation (you don't want to displace too much of the air around you with argon!), and again this will not work well with a flame. Evacuating the ampoules will probably be easiest. You can connect the open end of the filled amp to a vacuum (as described up above), then under vacuum, you use a torch to melt the neck of the ampule shut. The vacuum will keep the whole inside inert, and will automatically pull the hot glass in on itself to seal. You will also know if the seal is broken because there will be a loud pop! You can also test the quality of the vacuum with a handheld Tesla coil (http://www.arborsci.com/tesla-coil?gclid=CIiOifrwuMgCFdeRHwodEeEPCA)

I have been working on a method of using a stainless steel wire with a loop on its end that will close around an ampule and heat up using an electric current with a fair bit of voltage, heating it up under a vacuum or inert gas will not be a problem! I am still working out some stuff and it is still in a development stage, but I have shaped glass before using a wire but I am of course unsure if it will work as I hope it will.

If it does not work I will use the vacuum method, but I enjoy to experiment, it would be quite enjoyable if I was able to come up with a new, easy and practical way of sealing ampules, there will be quite a bit of tinkering but it is near completion but I got a pretty good idea in my head and a few sketches, and I am figuring that under an inert atmosphere the wire till not oxidize either which is quite good.

Choice of wire will of course matter as well, thickness of wire, how the loop is constructed - how it tightens around the ampule - etc..But the general idea is having the ampule in the chamber filled with my choice of gas, snaring a metal wire around the ampule in such a fashion that if pulled, it will tighten around the ampule. Heating the wire up slowly to the required temperature and then simply pulling on it to tighten the near-molten glass to seal.

Perhaps a vacuum is simpler or better, but as I said, trying out new things is always fun. Any thoughts why this method may end in failure?

I have been working on a method of using a stainless steel wire with a loop on its end that will close around an ampule and heat up using an electric current with a fair bit of voltage, heating it up under a vacuum or inert gas will not be a problem! I am still working out some stuff and it is still in a development stage, but I have shaped glass before using a wire but I am of course unsure if it will work as I hope it will.

If it does not work I will use the vacuum method, but I enjoy to experiment, it would be quite enjoyable if I was able to come up with a new, easy and practical way of sealing ampules, there will be quite a bit of tinkering but it is near completion but I got a pretty good idea in my head and a few sketches, and I am figuring that under an inert atmosphere the wire till not oxidize either which is quite good.

Choice of wire will of course matter as well, thickness of wire, how the loop is constructed - how it tightens around the ampule - etc..But the general idea is having the ampule in the chamber filled with my choice of gas, snaring a metal wire around the ampule in such a fashion that if pulled, it will tighten around the ampule. Heating the wire up slowly to the required temperature and then simply pulling on it to tighten the near-molten glass to seal.

Perhaps a vacuum is simpler or better, but as I said, trying out new things is always fun. Any thoughts why this method may end in failure?

hmm that's an interesting approach. You'll need to simultaneously heat at least 3–4 mm wide of glass up to "soft and tacky" temperatures before applying the pressure. Shaping glass is one thing, but have you ever successfully fused two pieces of glass together with this technique? If you can do that with the setup you have, I guess you're good to start experimenting with amps (I would seal at least half a dozen of em before trying to load one up with potassium or phosphorus!)

hmm that's an interesting approach. You'll need to simultaneously heat at least 3–4 mm wide of glass up to "soft and tacky" temperatures before applying the pressure. Shaping glass is one thing, but have you ever successfully fused two pieces of glass together with this technique? If you can do that with the setup you have, I guess you're good to start experimenting with amps (I would seal at least half a dozen of em before trying to load one up with potassium or phosphorus!)

Maybe just get one of these?

That machine was strangely mesmerizing!

Not with this technique per say, but something similar, once the glass is in its soft and tacky state, quickly increasing the temperature would work kind of like a spot weld, done it will a rod for other stuff but who knows, it may just blow up in my face.

Late arrival here, but I'd go for a vacuum, so you can honestly say that the ampoule only contains phosphorus or whatever.

I think you will have a problem with fluorine, which will attack the glass, and radioactive elements which may make it brittle.

I am quite fine with having gases protecting my samples, as long as my samples are pure!As for radiactive materials, I have been thinking that I should use radioactive minerals instead of elements, as most are illegal to acquire in my country, some are legal of course, but I am thinking to keep it all unified to simply use the minerals of all radioactive elements.

The Naked Scientists® and Naked Science® are registered trademarks.
Information presented on this website is the opinion of the individual contributors
and does not reflect the general views of the administrators, editors, moderators,
sponsors, Cambridge University or the public at large.